LXer have summarized the recent arguments against having no open ports after an install of Ubuntu.
Read the overview here at LXer
Or go for the source of the critisism
The “No Open Ports” policy: This policy (or at least the way many people interprete it) seems to be thought out by someone who doesn't have much experience with TCP/IP networking. While it might make sense to enforce this for application-level protocols like HTTP or FTP it doesn't make sense to apply it to transport-level protocols such as DHCP, DNS or in this case mDNS (the underlying protocol of Zeroconf/Avahi/Bonjour